The cell and cell organellesLife’s building blocks

What are cells?

The cell is the very smallest unit of living matter.

All living things are made up of one or more cells

There are an estimated 75-100 trillion cells in your body.

75,000,000,000,000-100,000,000,000,000 That’s a lot of zeros!

HistoryAnton Van Leeuwenhoek The microscope was invented by Anton Van

Leeuwenhoek, a Dutch biologist in the early 1600’s. Leeuwenhoek’s invention allowed him to see tiny living organisms in droplets of water.

Robert Hooke was the first person to name cells.

Hooke was looking at cork under the microscope and thought they looked like the rooms monks lived in called cells.

Matthias Schleiden – stated that all plants are made of cells. (1838)Theodor Schwann – discovered that all animals are made of cells too (1839).Rudolf Virchow – stated that all cells arise from the division of preexisting cells (1855).

Over the next 300 years…

The cell theory

A theory is a well-substantiated explanation of an aspect of the natural world that can incorporate laws, hypotheses and facts.

A theory is not a guess, but an idea that is supported by the work of many scientists usually over the course of many years.

Some of the scientists whose work helped to develop the cell theory are Hooke, Schlieden, Schwann, Brown and Virchow.

The 3 components of cell theory

1. The cell is the basic unit of structure for all living things. This means that all life is made of one or more cells.

2. The cell is the basic unit of function of all living things. This means that the life processes are carried out within the cells.

3. All cells arise from pre-existing living cells. This means that life doesn’t spontaneous appear from non-living matter.

Exceptions to cell theory.

As with other rules and theories, there are some exceptions.

1. Viruses. While they carry out some life processes, they aren’t made of cells.

2. Slime molds. During one part of their weird lifecycle, they are not differentiated into cells.

3. The very 1st cell. By definition, it couldn’t have arose from a pre-existing cell.

The organelles

A specialized structure within a cell, analogous to organs.

The term organelle literally means, “little organ”.

The first organelle to be discovered was the nucleus by an English biologist named Robert Brown.

It is in the organelles that the life processes are carried out.

The Nucleus

The nucleus is responsible for controlling and coordinating all cellular activity.

The nucleus contains our deoxyribonucleic acid (DNA).

The nucleolus A dark spherical mass located within the

nucleus. Composed of RNA. Creates Ribosomes.

The cytoplasm The jelly-like matrix of the cell. Mostly

water. All of the other organelles are suspended in

the cytoplasm. Sometimes referred to cystol.

Endoplasmic Reticulum Series of tubules running throughout the

cell. Aid in the transport of molecules. Rough E.R. has ribosomes in it’s

membrane and synthesizes proteins. Smooth E.R. has no ribosomes in it’s

membrane and synthesizes lipids.

Mitochondria The mighty mitochondria is the

powerhouse of the cell. Site of cellular respiration. Possess their own DNA and

replicate independently of the rest of the cell.

Thought to once have been a free living prokaryote.

Golgi Bodies (apparatus) Serve as temporary storage

sites for proteins and lipids. Modifies and packages

these molecules prior to secretion to other parts of the cell, or out of the cell.

Ribosomes Serve as the site of protein

synthesis. Ribosomes are found in the

membrane of rough endoplasmic reticulum as well as in the cytoplasm.

Vacuoles Storage sites for water, nutrients

and waste products. Small in animal cells and very

large in plant cells. In plant cells the central vacuole

helps to support the cell through hydrostatic pressure.

Lysosomes The suicide sac. Lysosomes digest worn out

organelles and help to break down proteins.

When a cell begins to break down, the lysosome swells up and bursts, digesting the entire cell. This is called autolysis.

Absent in plant cells.

Cell membrane Consists of a phospholipid bilayer which is

selectively permeable. Regulates what enters and exits the cell.

Centrioles Found in animal cells

only. These paired structure

are found next to the nucleus and aid in cell division.

Cell Wall Absent in animal cells. Made of cellulose, the cell wall helps to

support the plant cell and give it it’s shape. Cellulose is the most common organic

material on planet Earth.

Chloroplasts Found only in plant cells, the

chloroplasts are the site of photosynthesis.

Filled with chlorophyll, which gives green plants their color.

Chloroplasts contain their own DNA, just like mitochondria.

Perhaps another example of Endosymbiosis.

Review questions

Which organelles are found only in animal cells? Centrioles and lysosomes.

Which organells are found only in plant cells? Chloroplasts and Cell Walls.

Which two organelles possess their own DNA? Mitochondria and Chloroplasts.

Where in the cell is chromatin located In the nucleus.

Where are proteins modified and packaged in the cell? Golgi body.